In the future, it is foreseen that there will be a huge increase in the wireless data transmission using wireless networks and wireless connections. In order to handle this big increase in wireless data, the discussion is going towards a need for smaller cell sizes and more efficient network offloading opportunities by use of e.g. hotspots. Work is ongoing internally in some companies and also in open forums like 3rd Generation Partnership Project (3GPP) on how to enable efficient sharing of a RAN in order to allow different operators to share the RAN.
RAN sharing is not new, but in the future it is likely to even further share a RAN in order to keep operators cost low while still ensuring offloading by small cells (and still have a reasonable number of eNBs deployed in the environment). When a small cell RAN is shared (e.g. on 3.5 GHz carrier), it does not necessarily mean that a macro RAN (e.g. large area coverage) is shared among the operators that share the small cell RAN (hotspot RAN).
One problem arises in such configuration when idle mode (or similar) mobility is supported. Assuming that the idle mode mobility will be similar as in legacy, the mobility related information for idle mode mobility is based on broadcast information—i.e. information received by all user equipments (UEs). In such scenario, it is not possible to distinguish UEs e.g. based on their release version or their Home Public Land Mobile Network (HPLMN). Therefore, all UEs will receive all the broadcast information including also mobility related information.
As illustrated in FIG. 1, the problem arises when there are two UEs: UE 1 with subscription to PLMN 1 and UE 2 with subscription to PLMN 2. An access point (AP) is shared between the two PLMNs but the macro network is only accessible to UEs with correct subscription. That is, UE 1 cannot access eNB 2 deployed in PLMN 2 and UE 2 cannot access eNB 1 deployed in PLMN 1.
On the other hand, the mobility information broadcast by the AP has to include carrier information for both carriers of eNB 1 and eNB 2 (different carriers) as it has to be the information enabling mobility for both UE 1 and UE 2. The UEs cannot distinguish the mobility information and as a result, UE 1 will search, detect and measure cells from PLMN 2 (on carrier 2) in mobility evaluation although access is not allowed, and similarly UE 2 will search, detect and measure cells from PLMN 1 (on carrier 1) in mobility evaluation. This scenario leads to a number of unnecessary reselections and possibly also unnecessary signaling.
3GPP TS 36.304 describes the idle mode mobility of a UE, and 3GPP TS 36.331 defines the system information required for supporting idle mode reselection procedures. However, the 3GPP TS 36.331 assumes that an access network is connected to one PLMN that is under control of a single network operator. Therefore, the system information stated therein is not involving any information associated with PLMNs sharing a same RAN.